A West Australian man has failed in an appeal against his sentence for leading a jailhouse plot to start a doll-making business in Thailand as a front for a child sex ring.

Former teacher Mark Pendleton, 53, was in May found guilty of ringleading a plan involving other paedophiles - hatched when he was already serving a 16-year sentence for a string of sex offences against children.

He was handed a further jail term of more than six years.

His lawyer Simon Watters appealed the sentence, arguing it infringed the first limb of the totality principle, given that when Pendleton completes the sentence, he will still be subject to an indefinite detention order for dangerous sex offenders.

But on Friday, the full bench of WA's Court of Appeal dismissed the appeal.

Pendleton was in October sentenced to an additional four years behind bars after admitting to abusing two girls, one of whom he began raping when she was aged seven.

Pendleton had befriended the younger girl's mother in 1977, and abused her when he was supposed to be babysitting.

The second girl was 13 when Pendleton began abusing her in 1993, including raping her in a quarry.

The additional four-year jail term means Pendleton has been sentenced to a total of 27 years for sex offences - believed to be the longest total period for a pedophile in WA history.